Fault-responsive power system and method using active line current balancing

ABSTRACT

A fault-responsive power system and method using active line current balancing. First and second supply-side currents flowing from at least one power supply and into first and second conductor pairs, respectively, are measured. First and second remote-side currents flowing from the first and second conductor pairs and into first and second power converters, respectively, are measured. The outputs of the first and second power converters are electrically coupled together in parallel and deliver power to a load. The first and second remote-side currents are balanced in response to measurements of the first and second remote-side currents while power is being delivered. When a difference between the first and second supply-side currents at least meets a magnitude threshold, the first and second supply-side currents are reduced until the difference is less than the magnitude threshold.

TECHNICAL FIELD

The present disclosure is directed at a fault-responsive power systemand method using active line current balancing.

BACKGROUND

Generally speaking, power distribution systems can be put into either oftwo categories: those that rely on local powering, and those that relyon centralized power distribution.

For example, in an application such as powering remote RF radios inwireless telecom networks, local powering is implemented by installingpower conversion devices that tap electricity directly from the electricutility grid, and that then convert the AC electricity to lower voltageDC electricity that is usable for the intended loads. The majordrawbacks with this powering method are a relatively high cost ofacquiring multiple power meters, a longer turn-around time to get therequisite permitting for site acquisition, and the fact that this methodis not economically feasible and scalable for mass deployment because ofthe sheer volume of remote powered devices and equipment required.

Centralized power distribution is often preferred over local powering. Acentralized powering solution, also known as adopting a “hub and spoke”topology in industry, leverages a single connection to the electricutility grid from which a centralized power hub derives power. Thecentralized power hub then distributes the power to multiple remotelylocated network devices that can be installed thousands of feet awayfrom the centralized power source.

The industry typically implements centralized power distribution ineither of two ways. The more common method is “Remote FeedingTelecommunications-Voltage limited” (“RFT-V”). An emerging and newerapproach is referred to as “centralized bulk powering” or using a “FaultManaged Power System”.

In traditional RFT-V line powering, multiple loads in differentlocations are supplied remotely from a single centralized power sourceusing multiple conductor pairs in a one-to-one configuration; that is,one dedicated conductor pair or set of conductor pairs is used for eachremote load. To facilitate efficient delivery of power over longerdistances, the line voltage is usually boosted to +/−190 VDC or 380 VDCpeak-to-peak. However, the total permitted power per circuit is limitedto 100 W for safety reasons. In essence, the system is inherently saferdue to relatively low power operation, but this also creates a seriousdisadvantage: because of that power constraint, RFT-V line powering isnot cost effective for applications where the remote loads demand powerconsumption that exceeds that constraint. An example of such anapplication for which RFT-V is unsuitable is powering next-generationremote small cells for 5G cellular networking, which have a relativelyhigh power requirement and are deployed in high volumes for networkcoverage densification. This is because as the demand of powerincreases, so does the total number of conductor pairs and powerconversion devices. Other drawbacks for RFT-V line powering are thecable weight resulting from under-utilized conductor pairs and the factthat RFT-V infrastructure cannot be upgraded after initial installationwithout incurring a substantial capital expenditure.

In centralized bulk powering, instead of using power-limited circuits inwhich power is transmitted via multiple pairs of smaller wires,centralized bulk powering transmits an elevated voltage (e.g., anyvoltage between 300 to 450 VDC) over a single dedicated power conductorpair having a relatively larger diameter. Centralized bulk powering doesnot mandate a limit on the maximum power that can be transmitted overthe conductors. This enables multiple remote loads that can be poweredby just using a single conductor pair as opposed to multiple conductorpairs as in RFT-V. Consequently, the cost, weight, and the effectivediameter of the conductors are significantly reduced, which isbeneficial for both aerial and underground system installations. Inaddition, other advantages include the need for a lower number of powerconversion devices, connectors, junction boxes, and surge protectorfixtures.

SUMMARY

According to a first aspect, there is provided a system comprising:first and second power converters, wherein power outputs of the firstand second power converters are electrically coupled together inparallel; first and second supply-side current sensors for measuringfirst and second supply-side currents flowing into first and secondconductor pairs, respectively, from the at least one power supply; firstand second remote-side current sensors for measuring first and secondremote-side currents flowing into the first and second power convertersfrom the first and second conductor pairs, respectively; a currentbalancing controller for communicating with the first and second powerconverters and the first and second remote-side current sensors, andconfigured to balance the first and second remote-side currents flowinginto the first and second power converters in response to measurementsfrom the first and second remote-side current sensors; at least oneswitch electrically coupled to the at least one power supply andoperable to adjust magnitudes of the first and second supply-sidecurrents; and a fault management controller for communicating with theat least one switch and the first and second supply-side currentsensors, wherein the fault management controller is configured to:determine that a difference between the first and second supply-sidecurrents at least meets a magnitude threshold; and reduce the first andsecond supply-side currents in response to the difference at leastmeeting the magnitude threshold until the difference is less than themagnitude threshold by using the at least one switch.

The fault management controller may be further configured to determine aduration for which the difference between the first and secondsupply-side currents at least meets the magnitude threshold, and thefirst and second currents may be reduced in response to the differenceat least meeting the magnitude threshold and the duration at leastmeeting a duration threshold.

The at least one power supply may comprise a first power supply, and thefirst and second conductor pairs may both be powered by the first powersupply.

The first conductor pair may comprise a first conductor and a commonreturn line, and the second conductor pair may comprise a secondconductor and the common return line.

The at least one power supply may comprise a first power supply and asecond power supply, the first conductor pair may be powered by thefirst power supply, and the second conductor pair may be powered by thesecond power supply.

Each of the first and second power converters may comprise a DC-DCconverter comprising primary switches operable to control an inputimpedance or gain of the DC-DC converter. The DC-DC converter may beconfigured to receive a drive signal based on a control signal from thecurrent balancing controller and to adjust a switching frequency or theduty cycle of the primary switches in response to the drive signal.

Each of the first and second power converters may further comprise afeedback loop electrically coupled to an output of the DC-DC converterand configured to generate the drive signal based on a measurement of atleast one of voltage and current at the power output of the powerconverter, and on the control signal.

Each of the first and second power converters may further comprise afixed frequency or duty cycle pulse generator and be configured togenerate the drive signal based on an output of the fixed frequency orduty cycle pulse generator and on the control signal.

The current balancing controller may comprise: a current averagingcircuit electrically coupled to the first and second remote-side currentsensors for determining an average remote-side current; first and secondcurrent summing circuits each electrically coupled to the currentaveraging circuit and respectively electrically coupled to the first andsecond remote-side current sensors for respectively determining firstand second remote-side current errors between each of the first andsecond remote-side currents and the average remote-side current; andfirst and second compensation circuits respectively coupled to the firstand second current summing circuits for generating the control signalthat is sent to the first power converter and the control signal that issent to the second power converter.

The fault management controller may comprise: current summing circuitryelectrically coupled to the first and second supply-side current sensorsand configured to generate a current signal representing a differencebetween the first and second supply-side currents; and current signalqualifying circuitry comprising a comparator configured to compare thecurrent signal to the magnitude threshold and output a comparator outputsignal, wherein the fault management controller turns off the first andsecond supply-side currents based on the comparator output signalindicating that the current signal at least meets the magnitudethreshold.

The fault management controller may be further configured to determine aduration for which the difference between the first and secondsupply-side currents at least meets the magnitude threshold. The firstand second supply-side currents may be reduced in response to thedifference at least meeting the magnitude threshold and the duration atleast meeting a duration threshold, and the fault management controllermay further comprise signal on-delay circuitry comprising an on-delaytimer that is electrically coupled to the output of the comparator andthat is configured to output a fault signal when the comparator outputsignal has indicated that the current signal at least meets themagnitude threshold for the duration threshold.

The system may further comprise timer delay period circuitryelectrically coupled to the current summing circuitry and configured todetermine the duration threshold as a value that varies in response tothe difference between the first and second supply-side currents.

The timer delay period circuitry may be configured to determine theduration threshold from a lookup table indexed by different values ofthe difference between the first and second supply-side currents, orformulaically based on the difference between the first and secondsupply-side currents.

The at least one switch may comprise part of the at least one powersupply, and the fault management controller may be configured tomodulate the at least one switch to reduce the first and secondsupply-side currents to non-zero values.

The at least one switch may be opened to reduce the first and secondsupply-side currents to zero.

According to another aspect, there is provided a method comprising:measuring first and second supply-side currents flowing from at leastone power supply and into first and second conductor pairs,respectively; measuring first and second remote-side currents flowingfrom the first and second conductor pairs and into first and secondpower converters, respectively, wherein power outputs of the first andsecond power converters are electrically coupled together in parallel;balancing the first and second remote-side currents in response tomeasurements of the first and second remote-side currents; determiningthat a difference between the first and second supply-side currents atleast meets a magnitude threshold; and reducing the first and secondsupply-side currents in response to the difference at least meeting themagnitude threshold until the difference is less than the magnitudethreshold.

The method may further comprise determining a duration for which thedifference between the first and second supply-side currents at leastmeets the magnitude threshold, wherein the first and second supply-sidecurrents are reduced in response to the difference at least meeting themagnitude threshold and the duration at least meeting a durationthreshold.

The at least one power supply may comprise a first power supply, and thefirst and second conductor pairs may both be powered by the first powersupply.

The first conductor pair may comprise a first conductor and a commonreturn line, and the second conductor pair may comprise a secondconductor and the common return line.

The at least one power supply may comprise a first power supply and asecond power supply, the first conductor pair may be powered by thefirst power supply, and the second conductor pair may be powered by thesecond power supply.

Each of the first and second power converters may comprise a DC-DCconverter comprising primary switches operable to control an inputimpedance or gain of the DC-DC converter, and the method may furthercomprise for each of the first and second power converters: receiving acontrol signal from a current balancing controller; and generating adrive signal based on the control signal, wherein actively balancing thefirst and second currents comprises adjusting a switching frequency orduty cycle of the primary switches in response to the drive signal.

The method may further comprise, for each of the first and second powerconverters: measuring at least one of voltage and current at a poweroutput of the power converter; and generating the drive signal based ona measurement of at least one of voltage and current at a power outputof the power converter and on the control signal.

The method may further comprise, for each of the first and second powerconverters, generating the drive signal based on an output of a fixedfrequency or duty cycle pulse generator and on the control signal.

The method may further comprise, at the current balancing controller:determining an average remote-side current entering the first and secondpower converters from the first and second remote-side currents;determining first and second remote-side current errors between each ofthe first and second remote-side currents and the average remote-sidecurrent; and generating the control signal for the first power converterfrom the first remote-side current error and generating the controlsignal for the second power converter from the second remote-sidecurrent error.

The method may further comprise: determining a difference between thefirst and second supply-side currents; and determining the durationthreshold as a value that varies in response to the difference betweenthe first and second supply-side currents.

The duration threshold may be determined from a lookup table indexed bydifferent values of the difference between the first and secondsupply-side currents, or formulaically based on the difference betweenthe first and second supply-side currents.

Reducing the first and second supply-side currents may comprisemodulating switches in the at least one power supply such that the firstand second supply-side currents are reduced to non-zero values.

Reducing the first and second supply-side currents may comprise openingat least one switch to reduce the first and second supply-side currentsto zero.

According to another aspect, there is provided a non-transitory computerreadable medium having stored thereon computer program code that isexecutable by a processor and that, when executed by the processor,causes the processor to perform the method of any of the above aspectsor suitable combinations thereof.

This summary does not necessarily describe the entire scope of allaspects. Other aspects, features and advantages will be apparent tothose of ordinary skill in the art upon review of the followingdescription of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate one or more exampleembodiments:

FIG. 1 is a block diagram of a fault-responsive power system usingactive line current balancing, according to an example embodiment.

FIG. 2 is a block diagram of a fault-responsive power system usingactive line current balancing that comprises a standalone faultcontroller, according to an example embodiment.

FIG. 3 is a block diagram of a fault-responsive power system usingactive line current balancing that comprises a standalone faultcontroller and a three-conductor transmission line, according to anexample embodiment.

FIG. 4A depicts a flow of fault current for a scenario in which a personis touching a live conductor and ground, according to the prior art.

FIG. 4B depicts a flow of fault current for a scenario in which a personis touching two live conductors, according to the prior art.

FIG. 5 is a block diagram of the system of FIG. 2 depicting the flow ofline currents and their relationship to one another in the presence ofline-to-line fault caused by an external foreign body with certainimpedance, according to an example embodiment.

FIG. 6 is a block diagram of a current balancing controller shown inFIGS. 1-3 and 5 , according to an example embodiment.

FIGS. 7 and 8 are block diagrams of a DC-DC converter that may be usedas either power converter of the systems shown in FIGS. 1-3 and 5 ,according to various example embodiments.

FIG. 9 is a block diagram of a logic circuit implementation of the faultmanagement controller shown in FIG. 3 , according to an exampleembodiment.

FIG. 10 illustrates a graph of different regions that are categorizedinto safe and un-safe zones according to the IEC 60479-1 standard aswell as a table that shows the relationship between body current andallowable maximum duration.

FIG. 11 is a flowchart illustrating a method applied by the faultmanagement controller of FIGS. 2, 3, and 5 , according to an exampleembodiment.

FIG. 12 is a timing diagram illustrating a timing sequence of currentsignals and consequent fault response of the fault-responsive powersystem, according to an example embodiment.

FIG. 13 is a block diagram of a power supply that may be used in thesystem of FIG. 1 , according to an example embodiment.

FIG. 14 is a block diagram of a power supply that may be used in thesystem of FIGS. 2, 3, and 5 , according to an example embodiment.

FIG. 15 is a block diagram illustrating a point-to-point poweringarchitecture in which the system of FIGS. 1-3 and 5 may be used,according to an example embodiment.

FIG. 16 is a block diagram illustrating a bus powering architecture inwhich the system of FIGS. 1-3 and 5 may be used, according to an exampleembodiment.

FIG. 17 is a block diagram illustrating a complete system of linepowering for a telecom small cells application utilizing thepoint-to-point system architecture of FIG. 15 , according to an exampleembodiment.

DETAILED DESCRIPTION

Generally speaking, in a high voltage DC power transmission system thatuses centralized bulk powering one or more power supplies transmits highvoltage electricity to one or more DC-to-DC power converters. The one ormore DC-to-DC power converters convert the inbound electric power to alower voltage suitable for powering a load electrically coupled to anoutput of the one or more DC-to-DC power converters. One or more liveconductors acting as power transmission lines electrically couple theone or more power supplies to the one or more DC-to-DC power converters.Typical transmission distances span 200 ft (˜60 m) to 8 kft (˜2,400 m),for example. The currents entering the transmission lines from the oneor more power supplies are the “supply-side” currents, while thecurrents entering the one or more DC-to-DC power converters from thetransmission lines are the “remote-side” currents.

However, transmitting high voltage DC power poses a safety risk in thata person who inadvertently causes an electrical fault, such as bytouching two different live conductors, may receive a serious electricalshock. Ideally, the supply-side currents are equal to the remote-sidecurrents. However, if a person has caused an electrical fault along thetransmission lines, the supply-side and remote-side currents will differas a result of a certain amount of current being conducted through thebody of the person who caused the fault.

Various solutions to address the risk of electrical shock in highvoltage DC power transmission systems have been proposed. For example,one solution uses supply-side and remote-side controllers torespectively independently monitor the supply-side and remote-sidecurrents, and to communicate the remote-side current measurements fromthe remote-side controller to the supply-side controller. Thesupply-side controller compares the remote-side current measurement itreceives to the supply-side current it measures. If the currents differ,the supply-side controller concludes a fault is present and can shutdown power transmission. However, this solution requires a low-latencycommunication link to connect the two controllers, which can bepractically problematic.

Another example solution also uses supply-side and remote-sidecontrollers to respectively control a supply-side switch and aremote-side switch that, when both open, electrically isolate thetransmission lines. Pulsed power is delivered into the transmissionlines and when both switches are open and the transmission linesisolated, the supply-side controller monitors the voltage decay on thetransmission lines. A decay rate that exceeds a predefined thresholdindicates the presence of an electrical fault in response to which thesupply-side controller can shut down power transmission. However,delivering pulsed power requires relatively large power conductors,which increases costs and is a relatively inefficient use of materials.Relying on monitoring voltage decay also makes this solution susceptibleto parasitic capacitances and inductances.

Another example solution again uses supply-side and remote-sidecontrollers to respectively control supply-side and remote-sideswitches. In normal operation, pulsed power is delivered from thesupply-side to the remote-side by switching the remote-side switch onand off in synchronization with the signal coming from the supply-sidecontroller. When the remote-side switch is off (i.e., no power is beingdelivered into the one or more power converters), the supply-sidecontroller measures the magnitude of any supply-side current beingdelivered into the transmission lines. If this current exceeds apredefined threshold corresponding to an expected residual amount ofcurrent, the supply-side controller concludes that the current is due toan electrical fault and discontinues power transmission by opening thesupply-side switch. However, this solution again requires a low-latencycommunications link between the controllers so that the supply-sidecontroller knows when the remote-side switch is open, and pulsed powerdelivery requires a relatively large power conductor with thecorresponding drawbacks as described above.

A fourth solution again uses a supply-side controller and, instead of aremote-side switch, a current slope limiter. The current slope limiterdraws power from the one or more power supplies, with the supply-sidecontroller monitoring the supply-side current and controlling asupply-side switch that can be used to shut power off. The current slopelimiter is configured to draw current according to a pre-defined rampfunction having the same slope regardless of input and load dynamics. Ifcurrent is drawn in excess of this ramp function, the supply-sidecontroller concludes the excess draw is due to an electrical fault andshuts off the supply-side switch. However, this solution requires highprecision sensor devices and precise calibration, since it can bechallenging to distinguish between the pre-defined ramp function and anelectrical fault in real-world operating conditions; require a 2-stagepower conversion on the remote-side, as a pre-regulator is used for thecurrent slope limiter in addition to the one or more DC-DC convertersthemselves; and is transient event dependent in that the current slopeis only detectable at the moment the fault happens, regardless of theduration of the fault. This raises the risk that the event or transitionmay be missed in real-world operating conditions, particularly in thepresence of strong background noise.

In contrast to the above solutions, the systems and methods describedherein are directed at using active line current balancing to performfault detection. More particularly, one or more power supplies feed aload using two pairs of transmission lines. The transmission linesconduct power into DC power converters, the output of which areconnected in parallel to feed a load. The currents entering thetransmission lines from the one or more power supplies are “supply-side”currents, while the currents entering the DC power converters fromtransmission lines are the “converter-side” currents. Active currentbalancing is performed to cause the remote-side currents to besubstantially identical regardless of load or line voltage variations.“Active current balancing” refers to employing closed-loop feedbackcontrol using the converter-side currents as the controlled parameterand then modifying the switching frequency or duty cycle of the DC powerconverters, thereby effectively changing the input impedance or powercircuit gain to achieve balanced current. From the perspective of theone or more power supplies, absent an electrical fault they expect tosee a “mirrored current” between the pairs of transmission lines.However, some kind of electrical fault such as an external line-to-linefault resulting from a person touching both live conductors on eitherpair of the transmission lines results in a current imbalance that canbe detected on the supply-side. In response to such a current imbalance,power can be promptly reduced and, in some cases, shut off entirely. Thesystems and methods described herein accordingly do not require pulsedpower, which helps to keep conductor size relatively small compared toalternative solutions that rely on pulsed power; do not require acommunications link between supply-side and converter-side; and are lesssensitive to parasitics and noise than some of the alternative solutionsdescribed above.

Referring first to FIGS. 4A and 4B, there are depicted in FIG. 4A a flowof fault current for a scenario in which a person is touching a liveconductor and ground, and in FIG. 4B a flow of fault current for ascenario in which a person is touching two live conductors, bothaccording to the prior art.

Each of FIGS. 4A and 4B depicts a power supply A that comprises a pairof voltage sources F electrically coupled in series. Each of the voltagesources F is 200 V, and the positive terminal of one of the voltagesources F is labeled at +200 V while the negative terminal of the otherof the voltage sources F is labeled at −200 V. A ground faultinterrupter (“GFI”) G is electrically connected between the two sourcesF at 0 V to ground. An load C is electrically coupled to the +200 V and−200 V terminals of the power supply A and to ground.

In FIG. 4A, a person D commits a “line-to-ground fault” by touchingtheir hand to the +200 V transmission line and their foot to ground.However, by virtue of the GFI G, body current B briefly flows from the+200 V terminal to the GFI G, which then detects and interrupts thecurrent flow by turning off the voltage sources (control circuit notshown) and thereby prevents the person D from experiencing a seriouselectrical shock.

In contrast, in FIG. 4B the person D causes a line-to-line fault bytouching the +200 V and −200 V transmission lines with their hands. Thisbypasses the GFI G, and consequently the line-to-line fault does notresult in current interruption. The power supply A continues to supply aload current E even during the fault, and the body current B travelingthrough the person D can result in a serious electrical shock.

This problem is averted using, for example, an example embodiment of afault-responsive power system 100 such as that depicted in the blockdiagram of FIG. 1 . The system 100 generally comprises a powertransmitter 102 electrically coupled to a power receiver 112 via a firstconductor pair 110 a and a second conductor pair 110 b. Moreparticularly, the power transmitter 102 comprises a first power supply104 a and a second power supply 104 b that are communicatively coupledvia a communication link 106. Each of the power supplies 104 a,bcomprises positive and negative terminals V0+ and V0−, with the positiveand negative terminals of the first power supply 104 a beingrespectively electrically coupled to first and second conductors 108 a,bthat comprise the first conductor pair 110 a, and with the positive andnegative terminals of the second power supply 104 b being respectivelyelectrically coupled to third and fourth conductors 108 c,d thatcomprise the second conductor pair 110 b. As shown in FIG. 1 , theequivalent line impedances of the first through fourth conductors 108a-d are respectively Z1, Z2, Z3, and Z4.

The power receiver 112 comprises a first power converter 124 a, a secondpower converter 124 b, and a current balancing controller 126 that isused for active line current balancing. Power outputs labeled VL+ andVL− on each of the first and second power converters 124 a,b areelectrically connected together in parallel and used to power a load122. The power receiver also comprises first and second remote-sidecurrent sensors 114 a,b located along the first and third conductors 108a,c to measure currents flowing into the first and second powerconverters 124 a,b from the first and second conductor pairs 110 a,b(“remote-side currents”), respectively. As discussed in further detailbelow, the current balancing controller 126 receives first and secondremote-side current signals 116 a,b representative of the magnitudes ofthe currents flowing into the first and second power converters 124 a,b,respectively; and from the first and second remote-side current signals116 a,b, the current balancing controller 126 determines first andsecond control signals 118 a,b and sends them to the first and secondpower converters 124 a,b, respectively. The first and second powerconverters 124 a in response adjust their input impedances or powercircuit gain accordingly to help ensure that the currents flowing intothe first and second power converters 124 a,b are substantially balanced(i.e., identical) within a certain tolerance threshold. The use ofclosed-loop feedback by the current balancing controller 126 in the formof the current signals 116 a,b to control the power converters 124 a,band balance the remote-side currents is referred to as “active linecurrent balancing”.

As discussed in further detail below in respect of FIGS. 2, 3, and 5 ,the power transmitter measures a first supply-side current and a secondsupply-side current respectively flowing into the first and secondconductor pairs 110 a,b from the power transmitter 102. Thecommunication link 106 is used to compare the first and secondsupply-side currents to each other. When the power transmitter 102determines that a difference between the first and second supply-sidecurrents at least meets the magnitude threshold, it concludes that thecurrent imbalance is due to a fault since in normal operation thecurrent balancing controller 126 keeps the remote-side currents (andconsequently the supply-side currents) in balance. Consequently, thepower transmitter reduces the first and second supply-side currents toless than the magnitude threshold and prevents a person who may havecaused a fault from being seriously harmed. While not depicted in FIG. 1, either of the power supplies 104 a,b may comprise an integrated faultmanagement controller to control the first and second supply-sidecurrents, as discussed for example in respect of FIG. 13 below.

Referring now to FIG. 2 , there is depicted another example embodimentof the fault-responsive power system 100. The system 100 of FIG. 2 isdepicted as being identical to that of FIG. 1 except the communicationlink 106 between the first and second power supplies 104 a,b of FIG. 1is shown as being implemented using voltage reduction circuitry 202. Thevoltage reduction circuitry 202 comprises a fault management controller113; first and second supply-side current sensors 204 a,b located alongthe first and third conductors 108 a,c to measure the first and secondsupply-side currents, respectively; and first and second switches 206a,b operable to control the first and second supply-side currents. Forexample and as discussed further below, in response to detecting a faultthe first and second switches 206 a,b may be modulated to reduce thesupply-side currents, or opened for a sufficiently long duration to shutoff the supply-side currents entirely. First and second supply-sidecurrent signals 212 a,b representative of the magnitudes of the firstand second supply-side currents are sent from the first and secondsupply-side current sensors 204 a,b to the fault management controller113, respectively. In normal operation absent a fault, the currentbalancing controller 126 keeps the remote-side currents in balancewithin the magnitude threshold, and the supply-side currents areconsequently also balanced within the magnitude threshold.

FIG. 5 shows the operation of the system 100 of FIG. 2 when a personcauses a line-to-line fault. The person causing the fault is representedin FIG. 5 as a resistor 502 electrically coupling the first and secondconductors 108 a,b together. The first and second supply-side currentsare respectively labeled i1 and i2, the first and second remote-sidecurrents are respectively labeled i3 and i4, and the body currenttraveling through the person causing the fault is labeled i5. In normaloperation, i5=0 A and i1=i2=i3=i4. However, in a fault condition,i1=i3+i5, while i3=i4=i2. Consequently, in a fault condition i1>i2 bymore than the magnitude threshold. The values of i1 and i2 are obtainedby the first and second supply-side current sensors 204 a,b andtransmitted to the fault management controller 113 via the first andsecond supply-side current signals 212 a,b, respectively. When the faultmanagement controller 113 determines that i1 and i2 differ by more thanthe magnitude threshold, it opens or modulates the first and secondswitches 206 a,b by sending the first and second switch control signals210 a,b, respectively, thereby shutting off the first and secondsupply-side currents and discontinuing power transmission or reducingthe currents to non-zero values until their differential is less thanthe magnitude threshold.

While the fault management controller 113 may reduce and in some casesshut off the supply-side currents immediately in response to determiningthat the difference between the first and second supply-side currents atleast meets the magnitude threshold, in at least some embodiments thefault management controller 113 may reduce or shut off the supply-sidecurrents only after that difference has at least met the magnitudethreshold for at least a duration threshold. This is depicted in theexample method 1100 of FIG. 11 , which is for performance by the faultmanagement controller 113.

In FIG. 11 , the method 1100 starts at block 1102 and proceeds to block1104 where the fault management controller 113 measures currents i1 andi2 (the first and second supply-side currents) and determines thedifference between them. At block 1106, the fault management controller113 determines whether the difference between i1 and i2 at least meetsthe magnitude threshold; if no, the fault management controller 113proceeds to block 1108 and sets itself to a normal (i.e., non-fault)state. The fault management controller 113 then proceeds back to block1104. This is as described above in respect of FIG. 5 for normaloperation.

In contrast to the description of FIG. 5 above, if the differencebetween i1 and i2 does at least meet the magnitude threshold the faultmanagement controller 113 when applying the method 1100 of FIG. 11 thendetermines whether the difference persists for at least a durationthreshold at block 1110 (e.g., the magnitude threshold may be 200 mA,and the duration threshold may be 10 ms). If no, the fault managementcontroller 113 determines that the system 100 is operating normally atblock 1108 and then returns to block 1104. However, if yes, the faultmanagement controller 113 proceeds to block 1112 where it determinesthat an external fault is present and consequently reduces and in atleast some embodiments shuts off the first and second supply-sidecurrents using the first and second switch control signals 210 a,b.After block 1112, the fault management controller 113 proceeds to block1114 where the method 1100 ends.

In at least some example embodiments, the fault management controller113 may comprise a processor communicatively coupled to a non-transitorycomputer readable medium that has stored on it computer program codethat is executable by the processor and that, when executed by theprocessor, causes the fault management controller 113 to perform theexample methods described above, such as the method 1100 of FIG. 11 .Alternatively, and as described further below, the fault managementcontroller 113 may be implemented using application specific circuitry.

Referring now to FIG. 3 , there is shown another example embodiment ofthe fault-responsive power system 100. The system 100 of FIG. 3 isdepicted as being identical to that of FIG. 2 except that instead of thefirst through fourth conductors 108 a-d transferring power from thefirst and second power supplies 104 a,b to the first and second powerconverters 124 a,b, only the first power supply 104 a is used. The firstconductor 108 a electrically connects the first power supply's 104 apositive terminal V0+ to the first power converter's 124 a positiveterminal VIN+, and the fourth conductor 108 d electrically connects thefirst power supply's 104 b negative terminal V0− to the first powerconverter's 124 a negative terminal VIN− and to the second powerconverter's 124 b negative terminal VIN−. Downstream (i.e., towards theremote-side) from the first switch 206 a, the third conductor 108 cbranches off from the first conductor 108 a and is electricallyconnected to the second power converter's 124 b positive terminal VIN+.Consequently, the first conductor pair 110 a comprises the first andfourth conductors 108 a,d, and the second conductor pair 110 b comprisesthe third and fourth conductors 108 c,d. The fourth conductor 108 daccordingly acts as a common return line for both of the conductor pairs110 a,b. As in the embodiments of the system 100 shown in FIGS. 1 and 2, the fault management controller 113 of the system 100 of FIG. 3receives the first and second supply-side current signals 212 a,brepresentative of the first and second supply-side currents, and inresponse to a measured current imbalance in excess of the magnitudethreshold (and optionally for longer than the duration threshold) thefault management controller 113 uses the first switch control signal 210a to open the first switch 206 a. As the first and third conductors 108a,c are shorted together downstream of the first switch 206 a, openingonly the first switch 206 a is sufficient to shut off the first andsecond supply-side currents. As mentioned above, as an alternative tosimply opening the first switch 206 a and keeping it open to shut offthe first and second supply-side currents entirely, the fault managementcontroller 113 may alternatively modulate the first switch 206 a toreduce the magnitudes of the first and second supply-side currents tonon-zero values such that their differential is less than the magnitudethreshold.

Referring now to FIG. 6 , there is shown a block diagram of the currentbalancing controller 126 according to an example embodiment. FIG. 6shows that the current balancing controller 126 receives as inputs thefirst and second remote-side current signals 116 a,b and, based on them,determines and outputs the first and second control signals 118 a,b tothe first and second power converters 124 a,b, respectively.

The current balancing controller 126 comprises a current averagingcircuit electrically coupled to the first and second remote-side currentsensors 114 a,b to receive the first and second remote-side currentsignals 116 a,b for determining an average remote-side current. Moreparticularly, the current averaging circuit comprising a current averagesumming circuit 602 that receives the first and second control signals118 a,b respectively representing magnitudes of the first remote-sidecurrent (i3 in FIG. 6 ) and the second remote-side current (i4 in FIG. 6). The current average summing circuit 602 sums those magnitudestogether and outputs the result to a divider circuit 604 to determine anaverage remote-side current (i-ave in FIG. 6 ).

The average remote-side current is input to a first current summingcircuit 606 a, which determines the difference between i-ave and i3. Theoutput of the first current summing circuit 606 a is accordingly a firstremote-side current error (i3-error in FIG. 6 ). The first remote-sidecurrent error is input to a first compensation circuit, which comprisesa first proportional-integral compensator 608 a that receives the firstremote-side current error and outputs a signal to a first periodequivalent circuit 610 a that determines the period equivalent of thefirst remote-side current error and outputs it as the first controlsignal 118 a. As discussed further below in respect of FIGS. 7 and 8 ,the first control signal 118 a accordingly represents a basis on whichto determine the period of the signal used to control primary switchescomprising part of the first power converter 124 a to adjust the inputimpedance or gain of the first power converter 124 a and consequentlythe first remote-side current.

The average remote-side current is also input to a second currentsumming circuit 606 b, which determines the difference between i-ave andi4 as a second remote-side error (i4-error in FIG. 6 ). The secondremote-side current error is input to a second compensation circuit thatcomprises a second proportional-integral compensator 608 b and a secondperiod equivalent circuit 610 b that determine and output the secondcontrol signal 118 b in a manner analogous to that described above forthe first control signal 118 a.

In lieu of using the first and second proportional-integral compensators608 a,b, in at least some alternative embodiments (not depicted)different types of compensators, such as modified proportional-integralor a 2-pole 2-zero compensator, may be used. Additionally, while in FIG.6 the first and second control signals 118 a,b are a period equivalent,in at least some alternative embodiments (not depicted) they mayrepresent a duty cycle when the control switches comprising part of thefirst and second power converters 124 a,b are controlled using pulsewidth modulation as noted further below.

The current balancing controller 126 may be implemented digitally using,for example, a microcontroller or digital signal processor with built-inmath co-processor to perform real-time calculations of the first andsecond remote-side current errors and related compensation parametersand to then generate the first and second control signals 118 a,b.

FIGS. 7 and 8 are block diagrams of either of the power converters 124a,b, according to additional example embodiments. In FIG. 7 , power atthe positive terminal of the power converters 124 a,b is rectified by adiode 702 and conditioned in series by a resonant LLC topologycomprising primary switches and an LLC resonant tank circuit 706,secondary rectifiers 708, and output filters 710; this may collectivelycomprise, for example, a 1500 W 400V-to-54V Full Bridge LLC ResonantDC-DC Converter. The primary switches of the circuit 706 are modulatedin response to a drive signal as discussed further below. Thismodulation controls the input impedance or gain of the power converters124 a,b, which accordingly adjusts the amount of current entering thepower converters 124 a,b.

The power converters 124 a,b use closed-loop feedback control. Moreparticularly, a current loop control circuit 712 receives the value ofthe current output by the power converters 124 a,b while a voltage loopcontrol circuit 714 measures the voltage across the output terminals VL+and VL− of the power converters 124 a,b using a voltage sensor 724. Thecurrent loop control circuit 712 determines the difference between thecurrent output by the power converters 124 a,b and a current reference732 (i.e., maximum current limit) at a summing circuit 734, and outputsthis difference as a current error (labeled Io-error in FIG. 7 ) to acompensator 736. The compensator 736 is shown as a proportional-integralcompensator, although in alternative embodiments (not depicted) thecompensator 736 may be of a different type, such as modifiedproportional-integral or a 2-pole 2-zero compensator.

Analogous to the current loop control circuit 712, the voltage loopcontrol circuit 714 determines the difference between the voltage outputby the power converters 124 a,b and a voltage reference 726 (i.e., finaloutput voltage setting) at summing circuit 728, and outputs thisdifference as a voltage error (labeled Vo-error in FIG. 7 ) to acompensator 730. The compensator 730 is shown as a proportional-integralcompensator, although in alternative embodiments (not depicted) thecompensator 730 may be of a different type, such as modifiedproportional-integral or a 2-pole 2-zero compensator.

The outputs of the current and voltage loop control circuits 712,714 aresent to a min/max selector block 716. The min/max selector block 716compares the signals received from the current and voltage loop controlcircuits 712,714, selects the signal that represents the maximumfrequency (when frequency modulation is used) or the minimum duty cycle(when pulse width modulation [“PWM”] is used), and relays that signal toa period equivalent circuit 718. The period equivalent circuit 718 isanalogous to the circuits 610 a,b discussed above and determines theperiod equivalency of the selected signal. That period equivalency issummed with the first control signal 118 a (for the first powerconverter 124 a) or the second control signal 118 b (for the secondpower converter 124 b) using summing circuitry 720, with the resultingsignal being converted into the drive signal at a modulator 722. Thedrive signal is used to control how the primary switches of the circuit706 are modulated, thereby adjusting the power converters' 124 a,b inputimpedance or gain and controlling the magnitudes of the supply-sidecurrents. As in FIG. 6 , as an alternative to the period equivalentcircuit 718 in at least some alternative embodiments (not depicted) thedrive signal may represent a duty cycle when the control switchescomprising part of the first and second power converters 124 a,b arecontrolled using pulse width modulation as noted further below.

While the power converters 124 a,b use parallel current and voltage loopcontrol circuits 712,714 in FIG. 7 , alternative embodiments (notdepicted) may use only one of the current and voltage loop controlcircuits 712,714 or series/cascading current and voltage loop controlcircuits 712,714.

FIG. 8 depicts an embodiment of the power converters 124 a,b that relieson a two-stage cascaded implementation as opposed to voltage and/orcurrent feedback loops as in FIG. 7 , with the result being the powerconverters 124 a,b of FIG. 8 are simpler to implement than those of FIG.7 . Each of the power converters 124 a,b comprises a first stage 804that receives the first and second remote-side currents, and a secondstage 806 electrically coupled to the output of the first stage. Theoutput of the second stage 806 comprises the power converters' 124 a,boutput terminals VL+ and VL−.

The second stage 806 comprises a standalone DC-DC converter. Like thepower converters 124 a,b of FIG. 7 , in the first stage 804 power at thepositive terminal of the power converters 124 a,b is rectified by adiode 702 and conditioned in series by a resonant LLC topologycomprising primary switches and an LLC resonant tank circuit 706,secondary rectifiers 708, and output filters 710. However, instead ofusing a feedback loop comprising the current loop control circuit 712and/or the voltage loop control circuit 714, the first stage 804implement open-loop control using a fixed frequency pulse generator 802that outputs a pre-defined and fixed frequency (or a fixed duty cycle inthe case of PWM). This frequency is input to the period equivalentcircuit 718 and summed with the first control signal 118 a (for thefirst power converter 124 a) or the second control signal 118 b (for thesecond power converter 124 b) using the summing circuitry 720, with theresulting signal being converted into the drive signal at a modulator722. The drive signal is used to control the input impedance of theprimary switches of the circuit 706 as described above in FIG. 7 .

FIG. 9 is a block diagram of a logic circuit implementation of the faultmanagement controller 113 shown in FIG. 3 , according to an exampleembodiment. The circuitry shown in FIG. 9 depicts the terminal for thefirst switch control signal 210 a and not the terminal for the secondswitch control signal 210 b as it does in FIG. 3 ; however, anotherterminal may be added and shorted to the terminal for the first switchcontrol signal 210 a in order to make the circuitry of FIG. 9 suitablefor use as the fault management controller 113 shown in FIGS. 1, 2, and5 .

In FIG. 9 , the fault management controller 113 receives as input thefirst supply-side current signal 212 a (labeled i1 in FIG. 9 ) from thefirst supply-side current sensor 204 a and the second supply-sidecurrent signal (labeled i2 in FIG. 9 ) from the second supply-sidecurrent sensor 204 b. The current signals 212 a,b are input to currentsumming circuitry 902, which generates a differential current signalrepresenting a difference between the first and second supply-sidecurrents. This current signal is input to current signal qualifyingcircuitry 904. This functionality may be implemented digitally using,for example, a microcontroller or digital signal processor, or usinganalog circuitry such as an op-amp.

The current signal qualifying circuitry 904 comprises absolute valueprocessing circuitry 918 that determines the absolute value of thedifferential current signal, and outputs a signal labeled i-fault inFIG. 9 to the positive terminal of a comparator 920. A signal labeledI_THRESHOLD in FIG. 9 , which corresponds to the magnitude threshold, isinput to the negative terminal of the comparator 920. The output of thecomparator 920 is driven high if the current signal at least meets themagnitude threshold and is otherwise driven low.

The comparator's 920 output is sent to signal on-delay circuitry 910. Inparticular, the comparator's 920 output restarts an on-delay timer 922that drives its output high when the duration threshold has passed. Thecomparator's 920 output and the on-delay timer's 922 output are bothinput to an AND gate 924. Consequently, only when both the comparator's920 output is high (indicating that the difference between the first andsecond supply-side currents at least meets the magnitude threshold) andthe on-delay timer's 922 output is high (indicating that the differencebetween the first and second supply-side currents has at least met themagnitude threshold for at least the duration threshold) is the outputof the AND gate 924 high. The output of the AND gate 924 is used as theoutput of the signal on-delay circuitry and acts as a “fault signal”that is the basis of the first switch control signal 210 a. Moreparticularly, the fault signal is input to a latch circuit 912, whichdrives an inverter 916. The output of the inverter 916 is driven low inresponse to the high fault signal, and the inverter's 916 output is usedas the first switch control signal 210 a. The output of the latchcircuit 912 remains low until the system 100 and consequently also thelatch circuit 912 is reset using the SYSTEM RESET signal.

The value of the duration threshold applied by the on-delay timer 922 isdetermined by the signal applied to its T_SET input by a selector switch914. The selector switch 914 is movable between a first state in whichit sets the T_SET input to a fixed delay and a second state in which itsets the T_SET input to an adaptive delay. The fixed delay is set to amaximum safe delay corresponding to the MAXIMUM DELAY signal of FIG. 9 .As discussed further in respect of FIG. 10 below, the maximum safe delayis typically set to between 5 ms to 10 ms or lower.

The adaptive delay is determined using timer delay period circuitry 908that is electrically coupled to the current summing circuitry 902 toreceive the current signal representing the difference between the firstand second supply-side currents. More particularly, in the embodiment ofFIG. 9 the absolute value of the current signal is input to rollingaverage process circuitry 906 (as an alternative to a rolling average, asliding window may be used, or alternatively the rolling average processcircuitry 906 may be omitted) that determines a rolling average of thecurrent signal over a pre-determined averaging window; this helps tosmooth out noise in the current signal. The rolling average is used asinput to the timer delay period circuitry 908, which may determine theduration threshold using, for example, a lookup table indexed byi-fault, or by performing a calculation at runtime based on i-fault, asdiscussed further in respect of FIG. 10 below.

Referring now to FIG. 12 , there is shown a timing diagram illustratinga timing sequence of the first and second supply-side current signalsrespectively labeled i1 and i2 and consequent fault response of thefault-responsive power system 100, according to an example embodiment.The timing diagram also shows the magnitude threshold labeled i-fault,the difference between the first and second supply-side current signalslabeled i1-i2, and the value of the first switch control signal 210 alabeled PWR_SW for which a high value represents the first switch 206 abeing closed and a low value represents the first switch 206 a beingopen. For each of the first and supply-side current signals, the averagecurrent is labeled i-ave on the diagram.

The time axis in FIG. 12 shows times t1, t2, t3, t4, and t5, for whicht1<t2<t3<t4<t5. Prior to t1, the first switch 206 a is closed as i1-i2does not meet or exceed i-fault. In particular, a first current surge1202 prior to t1 does not meet or exceed i-fault and consequently doesnot trigger a fault response from the system 100. Between t1 and t2, asecond current surge 1204 does meet or exceed i-fault for at least theduration threshold labeled Delay1, and consequently at t2 PWR_SW isdriven low, the first switch 206 a opens, and i1 and i2 go to zero. Thesystem is reset after t2 and resumes normal operation at t3 until t4.Between t4 and t5, a third current surge 1206 again meets or exceedsi-fault for at least the duration threshold labeled Delay 2, andconsequently PWR_SW is again driven low at t5, the first switch 206 aagain opens, and i1 and i2 again go to zero.

Delay1 is shorter than Delay2 because the duration threshold used inconnection with FIG. 12 is dynamic. More particularly, the faultmanagement controller 113 dynamically determines the duration thresholdbased on the rolling average of i1-i2 as described above in respect ofFIGS. 9 and 10 for example.

Referring now to FIG. 10 , there is shown a graph 1002 of fault currentvs. maximum allowable current flow duration time that includes differentregions that are categorized into safe and un-safe zones according tothe IEC 60479-1 standard, as well as a table 1008 that shows therelationship between body current and allowable maximum duration. Themaximum allowable duration may be used as, or as a basis fordetermining, the duration threshold.

Zones DC-1 and DC-2 of the graph 1002 are categorized as safe regionsand define the preferred operating zones for the system 100. DC-3 is theboundary between safe and un-safe regions, and this operating zone ispreferentially avoided by the system 100. DC-4 is an un-safe ordangerous operating zone.

In at least some embodiments, the fault management controller 113determines the actual value of any fault current, as opposed to othervalues used only as a proxy for the fault current (e.g. voltage decay, adifferent test voltage, change in current over time, etc.). The abilityto quantifiably measure the magnitude of the fault current permits thesystem to implement a relatively resilient protection method using avariable or adaptive reaction time for the duration threshold. Incertain situations, the ability to vary the duration threshold increasessystem reliability.

Points 1004 and 1006 respectively show examples of fixed maximumallowable duration times given a particular fault current. For example,point 1004 shows a maximum allowable duration of no more than 100 ms fora magnitude threshold of 30 mA, while point 1006 shows a maximumallowable duration of no more than 10 ms for a fault current of 100 mA.In prior art systems, which do not directly measure fault current or donot have a mechanism to quantify the actual fault current, the mostcommon approach is to shut off current within 5-10 ms of detecting afault, regardless of the magnitude of the fault current; thiscorresponds to the shortest time in the DC-2 region regardless of thedetectable fault current. The problem with this approach is that itmakes the protection circuit very sensitive and prone to false-positiveor nuisance tripping. This is particularly problematic in outdoorinstallations where the power distribution system itself is subject todifferent noise transients in the field and other real-worldelectro-mechanical events such as ground potential rise, inductivecoupling with other electrical conductors in proximity, and lightningsurge transients. In the context of line powering in an outside plant(“OSP”), the spurious noise and line transients are magnified at lightload conditions when the power transmission line is under-damped. Anunder-damped power transmission line does not easily suppress transientnoise. Therefore, it makes sense to increase the fault qualifying timeat no load or light load conditions to increase the likelihood that thefault event is valid and not just induced by any incidental noise asdescribed above. If the power system does not have the ability for itsprotection system to have an adaptive duration threshold as a functionof fault current, then practically the protection circuit must always bedesigned for worst-case scenario, which is the shortest reaction timepossible in order to guarantee compliance with safety standards. Thislimitation is alleviated and addressed by permitting a dynamic durationthreshold, such as discussed above in respect of FIG. 9 .

In other words, by being able to closely quantify the magnitude of faultcurrent, the duration threshold can be made more flexible, adaptive, ordynamic as set out in the corresponding current-time table 1008. Themaximum timer delay period of the table 1008, which effectivelycorresponds to the duration threshold, is calculated as a function ofthe measured body fault current and is defined by the slope 1010, whichcorresponds to operation in the DC-2 zone.

There are two ways in which the system 100 may be configured to use adynamic duration threshold in response to particular operatingconditions. The first approach is by using a lookup table as set out inthe “Static Value [Lookup Table]” column of the table 1008. This methodprovides a simpler design implementation for the control circuit;however, the resolution of the current-time parameters is dependent onthe granularity or number of the terms in the lookup table.

The second approach is by calculating the duration threshold at run-timebased on the following pre-defined equation:T_(DELAY)=7.293×10⁶*(I_(SENSED))^(−2.548) which is determined from theslope 1010. This returns a continuous value for use as the durationthreshold as a function of the sampled current I_(SENSED) discussedabove in respect of FIG. 9 . While evaluating this equation at runtimeprovides more granularity, it also consumes more resources from thecontroller in terms of processing power, memory, etc. The practicalconsequences of this downside can be mitigated using relatively fast andhigh-memory processing circuitry capable of floating-point operation,such as a suitable microcontroller (“MCU”) or digital signal processing(“DSP”) chips. Alternative embodiments may use a different and stillsuitable formula for determining T_(DELAY); for example, a fixed offsetmay be added to I_(SENSED) to ensure a safety margin, the equation maybe determined using a different value for the slope 1010 (for example ifan AC current signal is being used), and/or an application-specificformula may be used.

In brief, if the measured fault current is lower, then the durationthreshold can be made longer while still meeting the safe operatingzone. On the other hand, if the measured fault current is higher, thenthe duration threshold is made shorter in order to reduce the hazardouscondition of potential prolonged exposure in case of accidental contactfrom a person. An advantage of permitting an adaptive or dynamicduration threshold is that it makes the system 100 more resilient,robust, and flexible across a wider range of different applications.

Referring now to FIG. 13 , there is depicted a block diagram of thefirst power supply 104 a that may be used in the system 100 of FIG. 1 ,according to an example embodiment. An analogous construction may beused for the second power supply 104 b.

In FIG. 13 , 48 V (+48 V at one terminal and 0 V at the other terminal)is applied across the power supply's 104 a input terminals. The voltageis sequentially processed by input filters and protection 1302, primaryswitches 1304, secondary rectifiers 1306, output filters 1308, an activedummy load 1310, and a ground-fault protection circuit 1312. Examplecircuitry may comprise or be based on, for example, a 2000 W 48V-to-400VFull Bridge LLC Resonant DC-DC Converter. This circuitry acts as aDC-to-DC converter that converts the 48 V input signal to a suitableoutput voltage; for example, +190V and −190V representing VO+ and VO−respectively. The secondary rectifiers 1306, output filters 1308, activedummy load 1310, and ground-fault protection circuit 1312 collectivelycomprise a secondary output circuit 1316. The controller 1318 is alsocommunicatively coupled to the second power supply 104 b via thecommunication link 106.

The fault management controller 113 is integrated into a combinedDC-to-DC converter microcontroller and fault management controller 1318.The controller 1318 is electrically coupled to the primary switches 1304so as to generate and send to the primary switches a drive signallabeled “PWM Drive” in FIG. 13 that disables the primary switches 1304and thereby shut off the first supply-side current in response to afault. Alternatively, in accordance with a corresponding PWM Drivesignal, the switching operation of the primary switches 1304 can also bemodulated to reduce the output VO+ and VO− to a safe level (e.g., 60V orless) in response to a fault. The controller 1318 applies the same logicas described above in respect of the fault management controller 113.The controller 1318 obtains the value of the first supply-side currentvia a current sensor 1314 and obtains the value of the secondsupply-side current via the communication link 106 from the second powersupply 104 b.

The active dummy load 1310 is controllable by the controller 1318 inorder to provide a fast discharge on the output capacitors of the DC-DCconverter. This helps voltage across the capacitors comprising part ofthe DC-DC converter to quickly decay to zero particularly at light loadconditions, decreasing the likelihood of electrical shock.

The ground-fault protection circuit 1312 provides protection in theevent of a line-to-ground fault. The ground-fault protection circuit1312 may comprise, for example, a GFI or a high resistance midpointground system.

The communication link 106 connecting the first and second powersupplies 104 a,b permits them to be controlled by the one controller1318. In an alternative embodiment (not depicted), the DC-to-DCconverter is designed to have two identical but independent secondaryoutput circuits 1316; one of the secondary output circuits 1316 is forthe first power supply 104 a and the other is for the second powersupply 104 b. This implementation renders the communication link 106unnecessary.

Referring now to FIG. 14 , there is depicted a block diagram of thefirst power supply 104 a that may be used in the system of FIGS. 2, 3,and 5 , according to an example embodiment. An analogous constructionmay be used for the second power supply 104 b. Like the power supply 104a of FIG. 13 , in the power supply 104 a of FIG. 14 48 V (+48 V at oneterminal and 0 V at the other terminal) is applied across the powersupply's 104 a input terminals. The voltage is sequentially processed byinput filters and protection 1302, primary switches 1304, secondaryrectifiers 1306, output filters 1308, and a ground-fault protectioncircuit 1312. Example circuitry may comprise or be based on, forexample, a 2000 W 48V-to-400V Full Bridge LLC Resonant DC-DC Converter.This circuitry acts as a DC-to-DC converter that converts the 48 V inputsignal to a suitable output voltage; for example, +190V and −190Vrepresenting VO+ and VO− respectively. In contrast to the power supply104 a of FIG. 13 , the fault controller 113 is external to the powersupply 104 a as depicted in FIGS. 2, 3, and 5 . The power supply 104 aof FIG. 14 comprises a DC-to-DC converter microcontroller 1402 which canshut off or reduce power as described above using the drive signallabeled “PWM Drive” in FIG. 14 to shut off or modulate the switching ofthe primary switches 1304. In FIG. 14 , the microcontroller 1402 shutsoff the power in response to a signal from the ground-fault protectioncircuit 1312 while the fault management controller 113 handlesline-to-line faults.

Referring now to FIG. 15 , there is depicted a block diagram of apoint-to-point powering architecture for which an example embodiment ofthe system 100 may be used. More particular, FIG. 15 depicts firstthrough Nth power transmitters 102 a-n, power receivers 112 a-n, andloads 122 a-n. First through Nth conductor pairs 110 a_a-n and 110 b_a-nrespectively electrically couple the first through Nth powertransmitters 102 a-n to the power receivers 112 a-n, and the firstthrough Nth powered devices are respectively electrically coupled to thefirst through Nth loads 122 a-n.

Referring now to FIG. 16 , there is depicted a block diagramillustrating a bus powering architecture for which an example embodimentof the system 100 may be used. More particularly, the first powertransmitter 102 a power the first through Nth power receivers 112 a-nvia first through Nth junction boxes 1602 a-n. The first through Nthpower receiver 112 a-n respectively power the first through Nth loads122 a-n.

Referring now to FIG. 17 , there is depicted a block diagramillustrating a complete system of line powering for a telecom smallcells application utilizing the point-to-point system architecture ofFIG. 15 , according to an example embodiment. As in FIG. 15 , firstthrough Nth power transmitters 102 a-n respectively power first throughNth power receivers 112 a-n. The first through Nth power receivers 112a-n respectively power groups of loads: loads 1 a-c are powered by thefirst power receivers 112 a, loads 2 a-2 c are powered by the secondpower receivers 112 b, and loads Na-Nc are powered by the Nth powerreceivers 112 n. First through Nth conductor pairs 110 a_a-n and 110b_a-n respectively electrically coupled the first through Nth powertransmitters 102 a-n to the first through Nth power receivers 112 a-n.

The first through Nth power receivers 112 a-n and their loads arerespectively located at first through Nth remote sites 1702 a-n, whichare located remote from a power hub 1702 at which the first through Nthpower transmitters 102 a-n are located. The power transmitters 102 a-nreceive DC power from one or both of batteries 1706 and arectifier/battery charger 1704 located at the power hub 1702. Therectifier/battery charger 1704 receives power from an AC power grid1708.

The embodiments have been described above with reference to flow,sequence, and block diagrams of methods, apparatuses, systems, andcomputer program products. In this regard, the depicted flow, sequence,and block diagrams illustrate the architecture, functionality, andoperation of implementations of various embodiments. For instance, eachblock of the flow and block diagrams and operation in the sequencediagrams may represent a module, segment, or portion of code, whichcomprises one or more executable instructions for implementing thespecified action(s). In some alternative embodiments, the action(s)noted in that block or operation may occur out of the order noted inthose figures. For example, two blocks or operations shown in successionmay, in some embodiments, be executed substantially concurrently, or theblocks or operations may sometimes be executed in the reverse order,depending upon the functionality involved. Some specific examples of theforegoing have been noted above but those noted examples are notnecessarily the only examples. Each block of the flow and block diagramsand operation of the sequence diagrams, and combinations of those blocksand operations, may be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. Accordingly, asused herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises” and“comprising”, when used in this specification, specify the presence ofone or more stated features, integers, steps, operations, elements, andcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components, andgroups. Directional terms such as “top”, “bottom”, “upwards”,“downwards”, “vertically”, and “laterally” are used in the followingdescription for the purpose of providing relative reference only, andare not intended to suggest any limitations on how any article is to bepositioned during use, or to be mounted in an assembly or relative to anenvironment. Additionally, the term “connect” and variants of it such as“connected”, “connects”, and “connecting” as used in this descriptionare intended to include indirect and direct connections unless otherwiseindicated. For example, if a first device is connected to a seconddevice, that coupling may be through a direct connection or through anindirect connection via other devices and connections. Similarly, if thefirst device is communicatively connected to the second device,communication may be through a direct connection or through an indirectconnection via other devices and connections. The term “and/or” as usedherein in conjunction with a list means any one or more items from thatlist. For example, “A, B, and/or C” means “any one or more of A, B, andC”.

The controller 113 used in the foregoing embodiments may comprise, forexample, a processing unit (such as a processor, microprocessor, orprogrammable logic controller) communicatively coupled to anon-transitory computer readable medium having stored on it program codefor execution by the processing unit, microcontroller (which comprisesboth a processing unit and a non-transitory computer readable medium),field programmable gate array (FPGA), system-on-a-chip (SoC), anapplication-specific integrated circuit (ASIC), or an artificialintelligence accelerator. Examples of computer readable media arenon-transitory and include disc-based media such as CD-ROMs and DVDs,magnetic media such as hard drives and other forms of magnetic diskstorage, semiconductor based media such as flash media, random accessmemory (including DRAM and SRAM), and read only memory.

It is contemplated that any part of any aspect or embodiment discussedin this specification can be implemented or combined with any part ofany other aspect or embodiment discussed in this specification.

In construing the claims, it is to be understood that the use ofcomputer equipment, such as a processor, to implement the embodimentsdescribed herein is essential at least where the presence or use of thatcomputer equipment is positively recited in the claims.

One or more example embodiments have been described by way ofillustration only. This description is being presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the form disclosed. It will be apparent to persons skilled inthe art that a number of variations and modifications can be madewithout departing from the scope of the claims.

1. A system comprising: (a) first and second power converters, whereinpower outputs of the first and second power converters are electricallycoupled together in parallel; (b) first and second supply-side currentsensors for measuring first and second supply-side currents flowing intofirst and second conductor pairs, respectively, from the at least onepower supply; (c) first and second remote-side current sensors formeasuring first and second remote-side currents flowing into the firstand second power converters from the first and second conductor pairs,respectively; (d) a current balancing controller for communicating withthe first and second power converters and the first and secondremote-side current sensors, and configured to balance the first andsecond remote-side currents flowing into the first and second powerconverters in response to measurements from the first and secondremote-side current sensors; (e) at least one switch electricallycoupled to the at least one power supply and operable to adjustmagnitudes of the first and second supply-side currents; and (f) a faultmanagement controller for communicating with the at least one switch andthe first and second supply-side current sensors, wherein the faultmanagement controller is configured to: (i) determine that a differencebetween the first and second supply-side currents at least meets amagnitude threshold; and (ii) reduce the first and second supply-sidecurrents in response to the difference at least meeting the magnitudethreshold until the difference is less than the magnitude threshold byusing the at least one switch.
 2. The system of claim 1, wherein thefault management controller is further configured to determine aduration for which the difference between the first and secondsupply-side currents at least meets the magnitude threshold, and whereinthe first and second currents are reduced in response to the differenceat least meeting the magnitude threshold and the duration at leastmeeting a duration threshold.
 3. The system of claim 1, wherein the atleast one power supply comprises a first power supply, and wherein thefirst and second conductor pairs are both powered by the first powersupply.
 4. The system of claim 1, wherein the first conductor paircomprises a first conductor and a common return line, and wherein thesecond conductor pair comprises a second conductor and the common returnline.
 5. The system of claim 1, wherein the at least one power supplycomprises a first power supply and a second power supply, the firstconductor pair is powered by the first power supply, and the secondconductor pair is powered by the second power supply.
 6. The system ofclaim 1, wherein each of the first and second power converters comprisesa DC-DC converter comprising primary switches operable to control aninput impedance or gain of the DC-DC converter, wherein the DC-DCconverter is configured to receive a drive signal based on a controlsignal from the current balancing controller and to adjust a switchingfrequency or the duty cycle of the primary switches in response to thedrive signal.
 7. The system of claim 6, wherein each of the first andsecond power converters further comprises a feedback loop electricallycoupled to an output of the DC-DC converter and configured to generatethe drive signal based on a measurement of at least one of voltage andcurrent at the power output of the power converter, and on the controlsignal.
 8. The system of claim 6, wherein each of the first and secondpower converters further comprises a fixed frequency or duty cycle pulsegenerator and is configured to generate the drive signal based on anoutput of the fixed frequency or duty cycle pulse generator and on thecontrol signal.
 9. The system of claim 6, wherein the current balancingcontroller comprises: (a) a current averaging circuit electricallycoupled to the first and second remote-side current sensors fordetermining an average remote-side current; (b) first and second currentsumming circuits each electrically coupled to the current averagingcircuit and respectively electrically coupled to the first and secondremote-side current sensors for respectively determining first andsecond remote-side current errors between each of the first and secondremote-side currents and the average remote-side current; and (c) firstand second compensation circuits respectively coupled to the first andsecond current summing circuits for generating the control signal thatis sent to the first power converter and the control signal that is sentto the second power converter.
 10. The system of claim 1, wherein thefault management controller comprises: (a) current summing circuitryelectrically coupled to the first and second supply-side current sensorsand configured to generate a current signal representing a differencebetween the first and second supply-side currents; and (b) currentsignal qualifying circuitry comprising a comparator configured tocompare the current signal to the magnitude threshold and output acomparator output signal, wherein the fault management controller turnsoff the first and second supply-side currents based on the comparatoroutput signal indicating that the current signal at least meets themagnitude threshold.
 11. The system of claim 10, wherein the faultmanagement controller is further configured to determine a duration forwhich the difference between the first and second supply-side currentsat least meets the magnitude threshold, wherein the first and secondsupply-side currents are reduced in response to the difference at leastmeeting the magnitude threshold and the duration at least meeting aduration threshold, and wherein the fault management controller furthercomprises signal on-delay circuitry comprising an on-delay timer that iselectrically coupled to the output of the comparator and that isconfigured to output a fault signal when the comparator output signalhas indicated that the current signal at least meets the magnitudethreshold for the duration threshold.
 12. The system of claim 11,further comprising timer delay period circuitry electrically coupled tothe current summing circuitry and configured to determine the durationthreshold as a value that varies in response to the difference betweenthe first and second supply-side currents.
 13. The system of claim 12,wherein the timer delay period circuitry is configured to determine theduration threshold from a lookup table indexed by different values ofthe difference between the first and second supply-side currents, orformulaically based on the difference between the first and secondsupply-side currents.
 14. The system of claim 1, wherein the at leastone switch comprises part of the at least one power supply, and whereinthe fault management controller is configured to modulate the at leastone switch to reduce the first and second supply-side currents tonon-zero values.
 15. The system of claim 1, wherein the at least oneswitch is opened to reduce the first and second supply-side currents tozero.
 16. A method comprising: (a) measuring first and secondsupply-side currents flowing from at least one power supply and intofirst and second conductor pairs, respectively; (b) measuring first andsecond remote-side currents flowing from the first and second conductorpairs and into first and second power converters, respectively, whereinpower outputs of the first and second power converters are electricallycoupled together in parallel; (c) balancing the first and secondremote-side currents in response to measurements of the first and secondremote-side currents; (d) determining that a difference between thefirst and second supply-side currents at least meets a magnitudethreshold; and (e) reducing the first and second supply-side currents inresponse to the difference at least meeting the magnitude thresholduntil the difference is less than the magnitude threshold.
 17. Themethod of claim 16, further comprising determining a duration for whichthe difference between the first and second supply-side currents atleast meets the magnitude threshold, wherein the first and secondsupply-side currents are reduced in response to the difference at leastmeeting the magnitude threshold and the duration at least meeting aduration threshold.
 18. The method of claim 16, wherein the at least onepower supply comprises a first power supply, and wherein the first andsecond conductor pairs are both powered by the first power supply. 19.The method of claim 16, wherein the first conductor pair comprises afirst conductor and a common return line, and wherein the secondconductor pair comprises a second conductor and the common return line.20. The method of claim 16, wherein the at least one power supplycomprises a first power supply and a second power supply, the firstconductor pair is powered by the first power supply, and the secondconductor pair is powered by the second power supply.
 21. The method ofclaim 16, wherein each of the first and second power converterscomprises a DC-DC converter comprising primary switches operable tocontrol an input impedance or gain of the DC-DC converter, and furthercomprising for each of the first and second power converters: (a)receiving a control signal from a current balancing controller; and (b)generating a drive signal based on the control signal, wherein activelybalancing the first and second currents comprises adjusting a switchingfrequency or duty cycle of the primary switches in response to the drivesignal.
 22. The method of claim 21, further comprising, for each of thefirst and second power converters: (a) measuring at least one of voltageand current at a power output of the power converter; and (b) generatingthe drive signal based on a measurement of at least one of voltage andcurrent at a power output of the power converter and on the controlsignal.
 23. The method of claim 21, further comprising, for each of thefirst and second power converters, generating the drive signal based onan output of a fixed frequency or duty cycle pulse generator and on thecontrol signal.
 24. The method of claim 21, further comprising, at thecurrent balancing controller: (a) determining an average remote-sidecurrent entering the first and second power converters from the firstand second remote-side currents; (b) determining first and secondremote-side current errors between each of the first and secondremote-side currents and the average remote-side current; and (c)generating the control signal for the first power converter from thefirst remote-side current error and generating the control signal forthe second power converter from the second remote-side current error.25. The method of claim 17, further comprising: (a) determining adifference between the first and second supply-side currents; and (b)determining the duration threshold as a value that varies in response tothe difference between the first and second supply-side currents. 26.The method of claim 25, wherein the duration threshold is determinedfrom a lookup table indexed by different values of the differencebetween the first and second supply-side currents, or formulaicallybased on the difference between the first and second supply-sidecurrents.
 27. The method of claim 16, wherein reducing the first andsecond supply-side currents comprises modulating switches in the atleast one power supply such that the first and second supply-sidecurrents are reduced to non-zero values.
 28. The method of claim 16,wherein reducing the first and second supply-side currents comprisesopening at least one switch to reduce the first and second supply-sidecurrents to zero.
 29. A non-transitory computer readable medium havingstored thereon computer program code that is executable by a processorand that, when executed by the processor, causes the processor toperform a method comprising: (a) measuring first and second supply-sidecurrents flowing from at least one power supply and into first andsecond conductor pairs, respectively; (b) measuring first and secondremote-side currents flowing from the first and second conductor pairsand into first and second power converters, respectively, wherein poweroutputs of the first and second power converters are electricallycoupled together in parallel; (c) balancing the first and secondremote-side currents in response to measurements of the first and secondremote-side currents; (d) determining that a difference between thefirst and second supply-side currents at least meets a magnitudethreshold; and (e) reducing the first and second supply-side currents inresponse to the difference at least meeting the magnitude thresholduntil the difference is less than the magnitude threshold.